Expendable cores for forming undercut regions in die casting dies for high pressure die casting machines require special means for their support, location and positioning of said cores in said dies. First of all, these expendable cores must deteriorate after the casting has been formed in the die so that they will shake out of the casting easily. Thus, these cores previously have been composed primarily of sand with special binders and impenetrable and release coatings, such as the cores and coatings described in applicants' assignee's U.S. patents to Page 4,298,051 issued Nov. 3, 1981; 4,413,666 issued Nov. 8, 1983; 4,766,943 issued Aug. 20, 1988; Dybala et al 4,529,028 issued July 16, 1985 and Downing copending application S.N. 07/173,558 filed Mar. 23, 1988 and now abandoned. Also these coated cores must withstand the high pressures and temperatuers of molten metal, such as molten aluminum, in the die casting die until the molten metal or aluminum has solidified sufficiently to form the casting. Furthermore, the outer surface of the core must not stick to the casting or to the printout cavities or sockets in the die into which the printout portions of the core are placed before the partable dies are closed and hot metal is injected into the die.
These expendable cores may be placed in any one or more parts of the dies, that is, the drag, the cope or cover, and/or the slides. Usually they are located along the parting line of the die parts for each placement. Because of the relatively brittle composition of the cores, if they are positioned too rigidly in the printouts, the very closing of the die and/or the high pressure injection of the hot metal could cause fracture of the cores. Accordingly, a space is provided between the outside surface of the printout portion of the core and the inside surface of the printout cavity in the die so that the core loosely fits or floats in its position in the die. However, on the other hand, if the space or clearance is too great, the core may fall out and/or will not be properly located in the casting so that the casting may have a thinner wall on one side thatn the other. Thus the cores also must be centered in their printout cavities.
Previously there have been many supports for cores in castings for forming undercut regions in the castings, even including means for adjusting the position of the cores in the dies or molds. In die casting dies there have been placed pins with flat ends. often referred to as "Leroy" pins, which bridge about half of the space between the printout cavity and the printout portion of the core for restricting the movement of the core in the direction of draw or relative movement of the partable dies. Then, to prevent movement in other directions, centering pins have been employed which have tapered ends that fit in sockets or pockets in the printout portions of the cores. The surfaces of these tapered ends are parallel with adjacent preformed tapered surfaces in these pockets, so that these centering pins restrict movement of the cores in linear directions orthogonally to that of the previously mentioned Leroy pins. The fact that the centering pins cannot be made to wedge or contact the adjacent parallel surfaces in the pocket in the printout portion of the core without locating the cores so rigidly that it could be broken by the closing of the die, there also must be provided a space between these parallel surfaces. The forming of these centering pins with their special tapered surfaces and corresponding pockets with corresponding tapered surfaces in the printout portion of the cores, materailly complicate the adjustment and manufacture of both the dies and the cores.
Because of the looseness of the core in its printout cavities in the die, the molten metal also fills the space between the printout cavity and the printout portion of the core, forming a film or skull over the printout portions of the core. This film also tends to maintain the position of the core in the die, as well as to strengthen the printout portion of the core. In this latter respect, grooves have been provided in the printout cavity or in the surface of the printout portion of the core, or both, for further reinforcing the skull with ribs therein, formed by the molten aluminum as it fills the space and grooves between the printout portions of the core and the printout cavities.
Furthermore, there have been provided ridges at the neck of the printout portion of the core located at the parting line of the dies, which ridges reduce the thickness of the skull at its neck to form a breakoff ring. This permits easy removal of the printout portion of the core for access to the core for easy removal of the core.
Thus, many of the previously known means for locating an expendable core in the die of a die casting machine have certain disadvantages and it is the purpose of this invention to overcome at least some of these disadvantages.